But now he's posted a message on his Facebook page, to say thanks.
"For petitioning Watercare to let it stay; thanks to Watercare for being good fellas and letting it stay [and not pressing charges!]; and of course a huge thanks to the tens of thousands of people who left positive comments, likes and messages in response."
He told the Herald he lived nearby, and had gone up with his dog to see what people thought when they looked at it in person.
"At one point, there was a queue of people lining up to get a photo with it, which was really touching.
"Obviously it's not because it's a particularly brilliant artwork, but it's about everyone paying respects to Murray Ball, someone we grew up with.
"I did have a little tear in my eye as I finished it off, gave it a little pat as I finished."
Walsh said Ball was one of New Zealand's greatest cartoonists.
He was gutted when he heard Ball had died, and painted the tribute that night.
"He was a childhood hero. It was one of the comics I grew up with, after spending my summers on the farm.
"He definitely inspired me to start drawing comics, back in the day.
"When I look back at my school books, they're all covered with comics in every corner.
"I read every dog-eared copy of Footrot Flats multiple times, and it was an honour to create my own small tribute to his genius and the indelible imprint he left on life in these islands I call home."
Many have commented that the tribute is particularly fitting, as it is in a dog-friendly park with an off-leash exercise area.